This invention relates to transmissions having a continuously variable ratio unit combined with a planetary gear arrangement.
Continuously variable power transmissions have been proposed for use in automotive vehicles for more than one hundred years. These proposed transmissions include a continuously variable unit, usually a traction drive or V-belt, combined with a gearing arrangement, which can be either a planetary gear arrangement or a parallel axis arrangement or a combination thereof. The planetary gear arrangement may have one or more planetary gear sets. Most of the proposals have been for single mode type arrangements wherein all of the power passes through the CVU in a single forward mode, and in a reverse mode. A dedicated gearing mechanism is also required to provide a reverse range. A launch device, such as a coupling or a starting clutch is generally required.
Some of the more recent proposals have been for a single or dual mode geared neutral type transmission. To achieve a geared neutral condition, at least one planetary gear set must be used as a summing differential, wherein the speed from the transmission input and the CVU output are applied to two nodes of the gear set to provide a resultant speed at the third node of the gear set. The third node is the output node which is connected with the transmission output. When the CVU is set to a specific ratio, relative to the transmission input speed, the transmission output will be stationary regardless of the transmission input speed. This geared neutral condition eliminates the need for a starting device, such as a torque converter, when the vehicle is stopped. The vehicle is launched from this geared neutral condition by changing the CVU ratio gradually to change the resultant speed of the transmission output toward either the reverse or forward direction without the need for a starting device.
Another function of the summing differential is to combine the power flow from two parallel power paths within the transmission. One path is through the CVU and the other is through fixed ratio gearing, which is generally the more efficient path.
Geared neutral transmissions are inherently inefficient in the low mode due to recirculating power through the CVU. Most of the known CVU transmissions have all of the power passing through the CVU in the high mode, which also limits the transmission efficiency.
It is an object of the present invention to provide an improved continuously variable ratio transmission having two ranges of operation.
In one aspect of the present invention, a planetary gear arrangement having two interconnected planetary gear sets is disposed between an input shaft, a continuously variable unit, and a transmission output shaft.
In another aspect of the present invention, two torque transmitting mechanisms are disposed within the transmission to connect the output of the continuously variable unit with selected members of the planetary gear sets.
In yet another aspect of the present invention, the planetary gear set has one member continuously driven by the transmission input shaft and one member in each of the planetary gear sets continuously connected with the transmission output shaft.
In still another aspect of the present invention, the output portion of the continuously variable unit is connected with a member of the planetary gear arrangement to provide rotation of that member in a direction opposite to the directional rotation of the input member.
In yet still another aspect of the present invention, the output of the continuously variable unit is connected to a mechanical drive mechanism and a selectively engageable clutch to establish a rotary input to one member of the planetary gear arrangement in the same direction as the rotary input of the input shaft to the planetary gear arrangement.
In a further aspect of the present invention during a first mode of operation, a geared neutral condition, a reverse range of operation, and a forward range of operation are provided.
In a still further aspect of the present invention, a second mode of operation is provided during which the forward range of operation is extended and the power output of the transmission input shaft and the continuously variable unit are combined to provide a split power mode of operation.
In yet still another aspect of the present invention, the interchange from a first mode to the second mode occurs with a synchronous shift wherein the rotating components of the clutch to be engaged have a synchronous rotating speed during the interchange.
In yet still a further aspect of the present invention, the planetary gear arrangement is a four-node summing differential arrangement having two clutches which selectively allow two modes of operation wherein one mode provides a geared neutral and the other mode provides a high efficiency split power path between the transmission input and the transmission output.
In yet still a further aspect of the present invention, only one of the gear sets is active during the high mode of operation to provide greater efficiency.